Tentacles start swiping in the direction they first spawned. I haven't step foot in there since it became open for farming without limit. Typically you identify the last tentacle, stack for knockback+holy, run in the direction of the first swipe (the first one that spawned) and then you split for flare markers (don't run into the breath else zombification).

I believe the popular strat was exdeath = true north? So tanks and healers can position their black holes appropriately and rotate before stacking for holy (after fire explosions). DPS typically stood near exdeath for uptime (but not too close to blow each other up). Also don't run into black holes hidden by his cape because that was/is a thing. You just need to be situationally aware of where black holes spawned and tethered to who and where.